A touchscreen is a monitor, typically based either on Liquid Crystal Display (LCD) or Cathode Ray Tube (CRT) technology, that accepts direct screen input. The ability to accept screen input is facilitated by an external device, such as a light pen, or an internal device, such as a touch overlay and controller, that relays the X,Y coordinates of a screen interaction to a computer controlling the screen display.
Resistive LCD touch screen monitors and displays rely on a touch overlay, composed of a flexible top layer and a rigid bottom layer separated by insulating dots, attached to a touchscreen controller. Typically, the inside surface of each of the two layers is coated with a transparent metal oxide coating (ITO) that facilitates a gradient across each layer when voltage is applied. Pressing the flexible top sheet creates electrical contact between the resistive layers, producing a switch closing in the circuit. Control electronics coupled to the overlay alternate voltage between the layers and pass the resulting X and Y touch coordinates to the touchscreen controller. The touchscreen controller data is then passed on to the computer operating system for processing.
Resistive touchscreen technology possesses many advantages over other alternative touchscreen technologies, such as acoustic wave, capacitive, Near Field imaging, and infrared. Being highly durable, resistive touchscreens are less susceptible to contaminants that can adversely affect acoustic wave touchscreens. In addition, resistive touchscreens are less sensitive to the effects of scratches that can render resistive touchscreens inoperative. For industrial applications, resistive touchscreens are more cost effective than Near Field imaging touchscreens.
It is becoming increasingly common for portable electronic devices to make use of touch screen technology when providing a display. In such instances, a user typically presses upon the display, such as with a finger or other implement, to input data or make a selection from amongst data displayed on the touch screen. Resistive touch screen technology is often used to determine finger position on the screen. Capacitive finger position technology is increasingly utilized but requires careful calibration to distinguish between a “finger on the display” condition and a “click” event. In either case, active tactility is required for a proper user experience. By “active tactility”, it is meant that the display provides tactile feedback to a user to transmit information related to the input or selection of data. Absent such a tactile response, it can be difficult for a user to ascertain if an intended input or selection was registered by the device.
Traditional methods for providing tactile feedback include the physical construction of entry keys to provide a “click” upon successful engagement as well as piezo-electric elements to provide a return force or vibration in the event that a key is successfully pressed. When combined, it is common for the touch screen displays and tactile feedback elements to form separate, if complimentary, systems.
The requirements of implementing a touch screen display and a separate active tactile feedback in mobile electronic devices are often too demanding when employing traditional solutions. For example, the presence of a tactile feedback layer can add excessive size to a small display. One other drawback associated with traditional touch screens is the degradation of the visual output from the display due to the addition of resistive layers forming the touch sensor.
There therefore exists a need for a system providing both touch screen input ability and tactile feedback that is compact and which is compatible with the display devices of mobile platforms.